1. Field of the Invention
The present invention relates to a magnetic compass and more particularly, to such a magnetic compass that is usable in the dark.
2. Description of the Related Art
FIG. 6 is an exploded view of a magnetic compass 80 constructed according to U.S. Pat. No. 6,578,277. According to this design, the magnetic compass 80 comprises a compass body 81, an illuminant 82, a conductive copper ring 83, a battery set 84 (which is consisted of a plurality of flat cylindrical lithium batteries that are stacked one by one), a base 85, a top lid 86, and a push button 87. The base 85 comprises a receiving chamber 851 that accommodates the compass body 81, a battery chamber 852 that accommodates the conductive copper ring 83, and an illuminant chamber 853 that accommodates the illuminant 82. The battery set 84 is situated within the conductive copper ring 83. The illuminant 82 comprises a first terminal 821 suspending above the battery set 84 and a second terminal 822 electrically connected to the conductive copper ring 83. The top lid 86 is covered on the base 85, having a button hole 861 corresponding to the battery chamber 852. The push button 87 is mounted in the button hole 861 of the top lid 86 and supported on the first terminal 821 of the illuminant 82. When pressed the push button 87, the first terminal 821 of the illuminant 82 is forced into contact with the battery set 84, thereby closing the circuit of the battery set 84 and the illuminant 82, and therefore the illuminant 82 is turned on to emit light toward the periphery of the compass body 81. Therefore, the magnetic compass 80 is effectively usable under low light conditions.
Referring to FIG. 7 and FIG. 6 again, the inner diameter of the conductive copper ring 83 is greater than the outer diameter of the battery set 84 so that the battery set 84 can conveniently be put into or taken out of the battery chamber 852. However, the presence of a gap between the conductive copper ring 83 and the battery set 84 may cause contact failure, thereby resulting in unstable supply of electricity to the illuminant 82.